Distribution transformers are parts of the power system infrastructure. The power system infrastructure includes power lines, transformers and other devices for power generation, power transmission, and power delivery. A power source generates power, which is transmitted along high voltage (HV) power lines for long distances. Typical voltages found on HV transmission lines range from 69 kilovolts (kV) to in excess of 800 kV. The power signals are stepped down to medium voltage (MV) power signals at regional substation transformers. MV power lines carry power signals through neighborhoods and populated areas. Typical voltages found on MV power lines power range from about 1000 V to about 100 kV. The power signals are stepped down further to low voltage (LV) levels at distribution transformers. LV power lines typically carry power signals having voltages ranging from about 100 V to about 600 V to customer premises.
In the United States local distribution transformers typically feed anywhere from one to ten homes, depending upon the concentration of the customer premises in a particular area. A power distribution system for a given area may include many distribution transformers. Thus, the replacement costs and maintenance costs for distribution transformers can be a significant factor in the cost of power distribution.
One factor that adversely affects the life and operation of a distribution transformer is a power overload. A distribution transformer is rated to handle power signals within a given power range. Overloading a given distribution transformer may reduce the useful life of the transformer. In particular, an overload increases the temperature of the transformer windings, which in turn increases the temperature of the transformer insulation. A breakdown of the transformer's insulation, such as from the increased temperature, decreases the useful life of the transformer and increases the chances of a transformer failure. In fact the cause of most transformer failures is a breakdown of the insulation, so anything that adversely affects the insulating properties inside the transformer reduces transformer life. Overloading a distribution transformer is one of the prime causes of insulation breakdown. In brief, loading a transformer over its rating for an extended period of time or at multiples of its nameplate rating for a brief period of time will reduce the transformer's life expectancy.
One challenge to the efficient maintenance of a distribution transformer is that an overload can not be detected and monitored directly. An overload may be inferred from load flow models. Commonly however, it is when the transformer fails that an overload condition is specifically identified. Further, there are many different sized transformers (with correspondingly different power ratings) in a power distribution system. However, the specific size and rating of a specific transformer is not directly monitored. Instead the transformer size and rating typically is inferred based on statistical usage information. Accordingly, there is a need for detecting and monitoring overload conditions at the many distribution transformers in a power distribution system.